In the past two decades diesel engines have increased power output per cylinder two to three times, but fuel injection systems which require very precise tuning and reliability have remained practically unchanged. The traditional design of the fuel system of such diesel engines includes engine driven fuel pumps, individual plunger-type fuel pumps, fuel injectors, and different types of governors. Lately designers and manufacturers of diesel engines, particularly marine diesel engines, have tried to introduce different types of "electronic" controls to existing conventional injection systems, such as camshaft driven unit injector with electronically on-off controlled solenoid valves, or providing hydraulic actuators for conventional plunger-type fuel pumps. However, these recent improved fuel systems for diesel engines are more complicated, less controllable, unreliable, and uneconomical than heretofore. Practically, when the operating condition of the fuel pumps in these fuel systems is changed due to cam, plunger or valve wear, the injection process becomes difficult to control regardless of the type of the associated electronic control. Each cylinder of the engine with this kind of injection system acts as an individual engine. With this arrangement it is difficult to balance power distribution between cylinders. In multi-cylinder engines the power distribution between cylinders becomes uncontrollable which causes overloading of some cylinders and underloading of others. This results in failure of pistons, bearings, crankshaft, and other major engine parts and increased exhaust emissions. Variable injection time (VIT) devices using existing VIT controls to individual cylinders do not properly react to load and ambient conditions of various engine operations.
No engine or fuel injection equipment manufacturer heretofore has attempted to directly control automatically the load sharing between individual cylinders, emission quality, and other major operating engine parameters. An electronically controlled functional algorithm or formula based on on-off principles cannot adequately react and govern existing conventional types of fuel injection systems. The very short time, only a few milliseconds, available for injection in diesel engines and the very high injection pressure, 1,000-2,000 bars, do not permit the utilization of a responsive and reliable system based on the principles of conventional injection system elements. Fuel injection systems based on a crankshaft-camshaft drive and camshaft actuate fuel pumps are dynamically and hydraulically unresponsive, cannot be properly controlled, and react to changes which occur as a result of different load and ambient conditions during engine operation.
Other attempts to solve the problems associated with a fuel injection system operated from a crankshaft-camshaft drive have included a pilot injection system with two fuel injectors with different settings, or a complicated pre-injection pump arrangement. Both the pilot or pre-injection pump concept approaches have disadvantages since the high injection pressure (1,000-2,000 bars) controls helixes on the plungers and associated valves deteriorate due to cavitation. Conventional fuel injectors, by method of operation, are direct-acting relief valves. They operate on differential forces between fuel supply pressure and mechanical spring. In conventional fuel injection systems the load distribution between individual cylinders is uncontrollable. The failure of an individual fuel pump or fuel injector and related equipment on a multi-cylinder engine reduces the power of the engine which had been generated by the failed cylinder. The load which has been lost from the failed cylinder is distributed between the remaining normally operating cylinders. This causes uneven load distribution and overload to the entire engine which is created by variable speed governors. Variable speed governors, as analog devices, serve the purpose of maintaining a constant speed. So, in reaction to the failure of a single cylinder, variable speed governors increase fuel supply to the remaining operating cylinder causing overload and increasing torsional vibration and emissions of the engine. The disadvantages of such fuel systems have been proven over many years by different engine manufacturers and fuel systems based on these principles are usually complicated, relatively unreliable and expensive.
U.S. Pat. No. 4,957,085 dated Sep. 18, 1990 disclosed a fuel injection system in which a separate pressurized control fluid is utilized which is in fluid communication with a fuel injection valve to control fuel flow to the injector ports. However, the pumps for the fuel and the control fluid are driven by a cam on the engine camshaft. Also, there is no separate flow control member controlling the flow of fuel to the fuel injector valve upstream of the fuel injector valve. Fuel timing and fuel quantity are controlled by a camshaft driven fuel pump even though the fuel injector valve is subjected to a fluid pressure differential between pressurized control fluid and pressurized fuel.